Edible oils as obtained by expelling and/or solvent extraction often require extensive purification. Accordingly, mucilaginous matter is removed during a degumming step, and free fatty acids are removed during the chemical neutralisation step by reacting them with caustic soda under formation of soaps. Colouring compounds are removed during the bleaching step when oil is treated with an adsorbent such as bleaching earth, and malodorous compounds are removed during the deodorisation step. This latter step can also serve the purpose of removing free fatty acids and is then commonly referred to as the steam refining or physical refining step.
Several degumming processes have been developed. The simplest process is a water degumming process, which only removes hydratable phospholipids present in the crude oil. The water degumming process does not remove non-hydratable phospholipids, which consist of calcium and magnesium salts of phosphatidic acid. To remove the latter, several processes have been developed such as the acid degumming process disclosed in U.S. Pat. No. 4,049,686, the acid refining process disclosed in Israeli patent 60835, the SOFT degumming process employing ethylene diamine tetra acetic acid (EDTA) disclosed in WO 95/00609 and various enzymatic processes.
The oldest of these enzymatic degumming processes is disclosed in U.S. Pat. No. 5,264,367. According to this patent, triglyceride oil having a phosphorus content of 50 to 250 ppm, and which is therefore likely to have been water degummed, is treated at a pH of 4 to 6 with an aqueous solution of a phospholipase A1, phospholipase A2 or phospholipase B until the phosphorus content of the oil has been reduced to less than 5 ppm. The degumming process disclosed in U.S. Pat. No. 5,558,781 also employs phospholipase enzymes with A1, A2 or B activity and also uses a separation promoter. Another process is disclosed in U.S. Pat. No. 5,532,163 in which the amount of water used to dissolve the phospholipase, which can be a phospholipase A2, and to disperse the oil into fine droplets with an average size of 0.1 to 50μ is at least 30% by weight of the oil. The use of phospholipase from Aspergillus is disclosed in U.S. Pat. No. 6,001,640 whereby it is stated that this enzyme has both phospholipase A1 and phospholipase A2 activity. In U.S. Pat. No. 6,103,505 an isolated peptide is disclosed that exhibits phospholipase A activity; a method for hydrolysing fatty acid groups in phospholipids or lysophospholipids by treating said phospholipids with said polypeptide is also disclosed. Finally, a process to prepare an oil that is amenable to physical refining employing an enzyme with phospholipase A1 activity has been disclosed in US 2004/0005399. However, the above degumming processes have in common that they use enzymes that hydrolyse a fatty acid glycerol bond. Consequently, they catalyse the production of free fatty acids. During the degumming process, these free fatty acids will be concentrated in the oil being degummed from which they have to be removed as part of the refining process.
A phospholipase enzyme, which is known as phospholipase C, does not cause the formation of free fatty acids because this enzyme catalyses the hydrolysis of the bond between the acylglycerol and the phosphate group. Accordingly, it liberates diacylglycerols and compounds like choline phosphate from phospholipids and monoacylglycerols and phosphates from lysophospholipids.
Such phospholipases have been disclosed in U.S. Pat. No. 7,226,771, which document also mentions that these phospholipases can be used in degumming processes of crude oil containing some phospholipids by mixing the compound with the oil to be degummed in the presence of an amount of water of 0.5 to 5%. Finally, WO 2008/094847 discloses a method for degumming an oil composition comprising the steps of (a) providing an oil composition containing a quantity of phospholipids, (b) contacting said oil composition simultaneously with one or more phospholipase A enzymes and one or more phospholipase C enzymes, under conditions sufficient for the enzymes to react with the phospholipids to create phospholipid reaction products, and (c) separating the phospholipid reaction products from the oil composition, the remaining oil composition after the separation being a degummed oil composition whereby during the step (b) the reaction of one or more phospholipase A enzymes proceeds at a faster rate than it would in the absence of said one or more phospholipase C enzymes.
The above prior art patents all aim at degumming: treating an oil containing phospholipids in such a way that the phospholipids are removed from the oil so that a degummed oil with a low residual phospholipids content results. They do this by using enzymes to hydrolyse the phospholipids. This hydrolytic activity is also used in a different process that aims at the recuperation of glyceride oil contained in the gums resulting from degumming processes of triglyceride oils.
Such oil recuperation has also been disclosed in U.S. Pat. No. 2,678,327, which describes the admixing of a liquefied, normally gaseous hydrocarbon such as propane with the hydrated gums and maintaining the resulting mixture under sufficient pressure to retain said hydrocarbon in liquid form, bringing said mixture to a temperature producing a solvent phase containing said liquefied hydrocarbon and said oil and an aqueous phase containing said gums while said gums contain sufficient water to produce a liquid aqueous phase, separating said phases, recovering de-oiled gums from said aqueous phase and vaporising said hydrocarbon from said solvent phase to recover oil therefrom. However, the use of a normally gaseous hydrocarbon such as propane necessitates the installation to be explosion proof, which requires a considerable additional investment. Moreover, the liquefaction and evaporation of this hydrocarbon require energy and thus augment the operating cost of this recovery process. It is therefore doubtful if the savings resulting from the sale of the recuperated oil as crude oil will be large enough to cover these costs.
Accordingly, a process obviating the use of organic solvents has been disclosed in EP 1 624 046. It comprises the steps of (a) providing wet gums by water degumming a crude vegetable oil, (b) mixing said wet gums with water containing a phospholipidolytic agent, (c) allowing the mixture to separate into two or more phases, said two or more phase including at least an oily phase and an aqueous phase, and (d) recuperating said oily phase. The phospholipidolytic agents comprise acids and phospholipase enzymes.
When enzymes such as phospholipase A1, A2 or B are used in the process disclosed in EP 1 624 046, the phospholipids present in the gums liberate free fatty acids. Since these acids are oil-soluble they are recuperated as part of the oily phase. When this oily phase is subsequently refined, said free fatty acids are removed from the oily phase and although they can be sold as acid oil or fatty acid distillate and can be used in oleochemical applications or as raw material for the production of biodiesel, their value will be less than that of a refined triglyceride oil. Enzymes with a phospholipase C activity do not have this disadvantage. They liberate oil-soluble diacylglycerols and water-soluble phosphates and during subsequent refining of the oily phase, the diacylglycerols are not removed from the oil. Accordingly they can be sold at full refined oil value.
Accordingly, the use of enzymes with phospholipase C activity offers advantages over the use of enzymes with phospholipase A1, A2 or B activity but in practice, the enzymes with phospholipase C activity that are commercially available are membrane-bound and have the disadvantage that they are very difficult to disperse in the gums from which the oil has to be recuperated. Consequently, the oil recuperation process as disclosed in EP 1 624 046 can be slow and unpredictable when phospholipase C is used. This process is therefore in need of improvement with respect to speed and robustness.
Another disadvantage of enzymes with phospholipase C activity is their selective activity on hydratable phospholipids. Indeed, enzymes with phospholipase C activity are only able to catalyse the hydrolysis of hydratable phospholipids whereas enzymes with phospholipase A1, A2 or B activity are able to catalyse the hydrolysis of both non-hydratable and hydratable phospholipids. Therefore, in practice, the oil recuperation process as disclosed in EP 1 624 046 leads to the recovery of an oily layer that is enriched in free fatty acids (FFA) if enzymes with phospholipase A1, A2 or B activity are used or in diacylglycerols if enzymes with phospholipase C activity are used.